feat: add display UI with splash screen, dashboard, and RSSI sparkline

Implement full SSD1306 OLED display support:
- Splash screen on boot (1.5s) with project name, version, board
- Dashboard showing radio state, config, counters, RSSI/SNR
- RSSI history sparkline (64-sample ring buffer, 2px-wide bars)
- DisplayOn/DisplayOff host commands routed via dedicated channel
- Pure render functions against generic DrawTarget (no hardware coupling)
- Display on/off control bypasses radio task entirely

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/anyhow/tests/ui/temporary-value.stderr

@@ -0,0 +1,15 @@
+error[E0716]: temporary value dropped while borrowed
+ --> tests/ui/temporary-value.rs:4:22
+  |
+4 |     let _ = anyhow!(&String::new());
+  |             ---------^^^^^^^^^^^^^-
+  |             |        |
+  |             |        creates a temporary value which is freed while still in use
+  |             temporary value is freed at the end of this statement
+  |             argument requires that borrow lasts for `'static`
+  |
+note: requirement that the value outlives `'static` introduced here
+ --> src/kind.rs
+  |
+  |         M: Display + Debug + Send + Sync + 'static,
+  |                                            ^^^^^^^